1. Field of the Invention
This invention has relation to a pneumatic variable air volume controller for regulating the supply of conditioned air through a passage to a defined area; and particularly to a controller for achieving a linear relationship between a pneumatic signal from a thermostat in the defined area and the actual velocity of air flowing in the passage.
2. Description of the Prior Art
It is known to use a damper to control the flow of conditioned air through a passage or duct into a defined area to be treated by conditioned air, and to adjust the rate of such flow responsive to a pneumatic signal from a thermostat in the defined area, the thermostat signal being representative of the desired temperature in the area. This has been done by developing a first pneumatic pressure signal representative of the velocity pressure (total pressure minus static pressure) in the passage or duct, comparing this first signal pressure to a second pneumatic pressure signal from the thermostat, developing a third pneumatic pressure signal representative of the difference between the first two signals and supplying this third signal to a damper actuator to open or close a damper according to such pressure differences. See the following U.S. Pat. Nos.: 3,719,321, granted to McNabney on Mar. 6, 1973; U.S. Pat. No. 3,941,310, granted to Traviglo et al on Mar. 2, 1976; U.S. Pat. No. 4,077,567, granted to Ginn et al on Mar. 7, 1978; U.S. Pat. No. 4,384,492, granted to Kreuter on Mar. 23, 1983; and U.S. Pat. No. 4,467,956, also granted to Kreuter but on Aug. 28, 1984.
It is known that the actual air velocity in a duct (in feet per minute, for example) varies as the square root of the air velocity pressure in the duct.
In the past, in order to achieve a linear relationship between the actual air velocity in a duct carrying conditioned air and a pneumatic pressure signal from a thermostat, a first pneumatic pressure signal representative of the square root of the velocity pressure was developed and compared in a differential pressure measuring device to a second pneumatic pressure signal from the thermostat. See U.S. Pat. No. 4,384,492, granted to Kreuter on May 24, 1983. The disclosure of this patent is incorporated herein by this reference to it. Such a structure proved very effective; but it is too expensive for certain applications. For that reason, among others, the structure of the present invention was developed.
Other patents known to the applicant and those in privity with him and which show some of the isolated elements which are part of the combination making up this present invention are U.S. Pat. Nos.: 4,263,931, granted to Bramow et al on April 28, 1981; and U.S. Pat. No. 4,264,035, granted to Maxon et al, also on Apr. 28, 1981.
Patents which appear to be at least somewhat related to the field of the invention are: U.S. Pat. Nos.: 4,147,298, granted to Leemhuis on Apr. 3, 1979; U.S. Pat. No. 4,406,397, granted to Kamata on Sept. 27, 1983; and U.S. Pat. No. 4,422,571, granted to Bowman on Dec. 27, 1983. They are not believed to be as pertinent as the prior art discussed above.